This invention relates to a method of joining a first component made of plastic to a second component made of plastic.
Such a method is known from European Patent 0 567 702 B1, for example. To connect a first plastic component, such as an intake manifold of an intake manifold system of an internal combustion engine to a second plastic component such as a flange of this intake manifold system, the first component having at least one connecting section on which the connection to the second component is to be created is introduced into an injection mold. The second component is then formed by integral molding of plastic onto the connecting section of the first component, whereby one surface of the connecting section is at least partially wetted by plastic of the second component.
Through appropriate shaping of the connecting section, in particular through an increasing wall thickness and a suitable embedding of the connecting section in the plastic material of the integrally molded component, where the integrally molded component largely encompasses or surrounds the connecting section of the other component, a formfitting connection that can withstand relatively high static stresses can be established between the components.
U.S. Pat. No. 5,266,262 describes blow-molded intake manifolds onto which a common flange is integrally molded. The intake manifolds have connecting sections which are embedded in the plastic of the flange in integral molding. Ring-shaped projections extending outward are formed on these connecting. Sections and are anchored like a barb in the integrally molded flange in a form-fitting manner. The strength, in particular the tensile strength, of this connection is increased in this way.
U.S. Pat. No. 4,752,208 describes a method which is used for integral molding of a coupling sleeve onto a corrugated tube hose. The injection mold and the injection process are coordinated so that at least two corrugations on the end of the corrugated tube to be sheathed are compressed, with the one corrugation sealing the injection mold while the other corrugation is embedded as an anchor in the integrally molded sheathing. In addition, the parameters are selected in this process so that the sheathed corrugated tube end softens, fuses at the surface and forms a bond with the integrally molded sheathing. However, the sheathed corrugated tube end and the compressed corrugations are retained as such.
In order for such a connection to have a long lifetime even under high-frequency dynamic stresses and to be able to guarantee that the connection will be leakproof even at high pressures during this lifetime, the components must be bonded together. To this end, the first component onto which the second component is to be integrally molded may be heated before being Inserted into the injection mold so that the plastic softens or begins to fuse in the area of the connecting section. In this condition, the first component can then be inserted into the infection mold. Then the molding operation is performed, with the molten injected plastic and the partially fused plastic at the surface of the first component being fused together. The desired intimate bonding connection is formed on solidification of the melts which have thus been mixed in this way. The plastics to be joined by bonding in this way are preferably compatible and are based on the same basic substance.
However, such a method cannot be used when at least one of the components is made of a plastic which has a relatively small or narrow temperature range for processability of the melt thereof. In other words, there as only a relatively short distance between a minimum melt temperature, which is the minimum necessary for processing of the melt, and a maximum melt temperature above which it is no longer possible to process the melt as intended. This is the case with polyamide [nylon] plastics, for example. For example, if the first component is made of such a plastic, then the melt on the connecting section which is formed by heating will have cooled again by the start of the injection molding operation to the extent that the desired bonded connection cannot be achieved consistently. In addition, it is relatively complicated to heat or partially fuse the first component and transfer it to the injection mold. If, in contrast with this, the component to be integrally molded is made of a plastic of the above-mentioned type, the melt compound will rapidly cool to a temperature below the aforementioned minimum melt temperature as soon as the melt compound comes in contact with the first plastic component in the integral molding operation.
The present invention relates to the object of designing a method of the type such that a bonded connection can be established relatively inexpensively between two plastic components even if the plastic of one component and/or the other has a relatively narrow temperature range for processability of its melt.
This object is achieved according to the present invention.
This invention is based on the general idea of orienting the thermal energy transferred from the integrally molded plastic to the first component through the design of bonding bodies at the surface of the connecting section of the first component in such a way that these bonding bodies thus melt and can fuse with the integrally molded plastic. Thus, due to this controlled thermal conduction, preferred melting zones are formed on the connecting section where surface melting takes place rapidly enough to form the desired high-quality bonded connection of the two components.
According to a preferred embodiment, the bonding bodies may be formed by elevations that are formed on the component at the time of its manufacture and project away from the surface of the connecting section, so that the bonding bodies are formed in one piece with the connecting section. Due to the fact that the bonding bodies are taken into account in the production and design of the first component, there is no increase in cost for production of the first component. In addition, due to their integration into the shape of the first component, these bonding bodies are connected to it in a highly effective manner. Since the bonding bodies project away from the surface of the connecting section, the heat transferred to the integrally molded plastic on coming in contact with the latter cannot be dissipated rapidly enough over the connecting section or the first component, so there is a buildup of heat with the desired result that the plastic of the first component melts at the surface in the area of the connecting section at the bonding bodies, permitting fusion with the integrally molded plastic.
With the method proposed according to this invention, it is also possible to integrally mold a component which, as an injection molded part, consists of a plastic which has a low viscosity in the melt, onto a component made of a plastic which has a high viscosity in the melt. The highly viscous plastic on the bonding bodies is heated and liquefied to the extent that it can mix or bond with the low-viscosity integrally molded plastic. In particular, it is thus possible to design the first component as a blow-molded part, in other words, the first component is produced by a blow-molding method. In order for this to be possible, the first component must be made of a high-viscosity plastic.
To improve the surface melting of the bonding bodies, the temperature at which the plastic of the second component is injected into the injection mold, i.e., the Injection temperature, is selected so as to be close to the upper limit of the temperature range in which an injection molding method can be carried out with this plastic. This measure increases the amount of heat that can be transferred from the injected plastic to the first component.
Additional important features and advantages of the method according to this invention are derived from the subordinate claims, the drawings and the respective description of the figures on the basis of the drawings.
It is self-evident that the features mentioned above and to be explained below can be used not only in the combination described here but also in any other combinations or alone without going beyond the scope of the present invention.